Integration of gallium nitride thin films with dissimilar substrate materials by wafer bonding and laser lift-off

Enhancing integrated microsystem functionality requires the joining of dissimilar materials in which the integration process may be accomplished through a variety of techniques. These techniques include bonding of discrete elements, wafer bonding, lift-off and transfer, and direct thin-film deposition. In this dissertation, the development of a new integration tool, laser lift-off (LLO) will be presented. By combining the LLO process with wafer bonding techniques, the integration of GaN thin films onto dissimilar substrate materials was demonstrated.; Successful separation of GaN from GaN/sapphire structures was accomplished using a single 38 ns KrF excimer (248 nm) laser pulse directed through the transparent sapphire substrate. For fluences between 400--600 mJ/cm 2. the absorption at the GaN/sapphire interface induces a highly localized, rapid thermal decomposition of the GaN, yielding metallic Ga and N2 gas. Heating the interface above the melting point of Ga (30°C) allows the separation of the GaN from the sapphire. Characterization of the GaN films after LLO by scanning electron microscopy, atomic force microscopy, x-ray diffraction and photoluminescence showed that the separation process does not degrade the structural and optical qualities of the GaN films.; Thermal calculations were made using analytical solutions to the heat transfer equation, and confirmed with finite element analysis, to predict the laser fluence needed for LLO. These calculations showed the GaN decomposition temperature (∼1000°C) was exceeded in a 100 nm thick GaN interfacial layer at an incident fluence of 600 mJ/cm2, the experimentally observed lift-off fluence threshold. Thermoelastic stress analysis was also performed to predict a process window to minimize the possibility of GaN structural degradation during the LLO process.; By incorporating a low-temperature Pd-In bonding process with LLO, GaN thin films were successfully transferred from sapphire onto Si, GaAs, and polyimide substrates. The intermetallic compound PdIn3 (T m = 664°C), formed from a Pd-In bilayer after a 200°C anneal, was used as the bonding interface. The integration process was completed after removing the sapphire substrate by LLO. By utilizing these process integration tools, the fabrication of a vertical InGaN blue light-emitting diode, prefabricated on sapphire and subsequently transferred onto Si, was demonstrated.